/**
* /// Reverses an fst
* ///
* /// @param fst the fst to reverse
* /// @return the reversed fst
*/
public static Fst Get(Fst fst)
{
if (fst.Semiring == null)
{
return(null);
}
ExtendFinal.Apply(fst);
Semiring semiring = fst.Semiring;
Fst res = new Fst(fst.GetNumStates());
res.Semiring = semiring;
res.Isyms = fst.Osyms;
res.Osyms = fst.Isyms;
State[] stateMap = new State[fst.GetNumStates()];
int numStates = fst.GetNumStates();
for (int i = 0; i < numStates; i++)
{
State _is = fst.GetState(i);
State s = new State(semiring.Zero);
res.AddState(s);
stateMap[_is.GetId()] = s;
if (_is.FinalWeight != semiring.Zero)
{
res.SetStart(s);
}
}
stateMap[fst.Start.GetId()].FinalWeight = semiring.One;
for (int i = 0; i < numStates; i++)
{
State olds = fst.GetState(i);
State news = stateMap[olds.GetId()];
int numArcs = olds.GetNumArcs();
for (int j = 0; j < numArcs; j++)
{
Arc olda = olds.GetArc(j);
State next = stateMap[olda.NextState.GetId()];
Arc newa = new Arc(olda.Ilabel, olda.Olabel,
semiring.Reverse(olda.Weight), news);
next.AddArc(newa);
}
}
ExtendFinal.Undo(fst);
return(res);
}
/**
* /// Calculates the n-best shortest path from the initial to the final state.
* ///
* /// @param fst
* /// the fst to calculate the nbest shortest paths
* /// @param n
* /// number of best paths to return
* /// @param determinize
* /// if true the input fst will bwe determinized prior the
* /// operation
* /// @return an fst containing the n-best shortest paths
*/
public static Fst Get(Fst fst, int n, Boolean determinize)
{
if (fst == null)
{
return(null);
}
if (fst.Semiring == null)
{
return(null);
}
var fstdet = fst;
if (determinize)
{
fstdet = Determinize.Get(fst);
}
var semiring = fstdet.Semiring;
var res = new Fst(semiring);
res.Isyms = fstdet.Isyms;
res.Osyms = fstdet.Osyms;
var d = ShortestDistance(fstdet);
ExtendFinal.Apply(fstdet);
var r = new int[fstdet.GetNumStates()];
var queue = new PriorityQueue <Pair <State, float> >(new CustomComparer(d, semiring));
var previous = new HashMap <Pair <State, float>, Pair <State, float> >(fst.GetNumStates());
var stateMap = new HashMap <Pair <State, float>, State>(fst.GetNumStates());
var start = fstdet.Start;
var item = new Pair <State, float>(start, semiring.One);
queue.Add(item);
previous.Put(item, null);
while (queue.Count != 0)
{
var pair = queue.Remove();
var p = pair.GetLeft();
var c = pair.GetRight();
var s = new State(p.FinalWeight);
res.AddState(s);
stateMap.Put(pair, s);
if (previous[pair] == null)
{
// this is the start state
res.SetStart(s);
}
else
{
// add the incoming arc from previous to current
var previouState = stateMap.Get(previous.Get(pair));
var previousOldState = previous.Get(pair).GetLeft();
for (var j = 0; j < previousOldState.GetNumArcs(); j++)
{
var a = previousOldState.GetArc(j);
if (a.NextState.Equals(p))
{
previouState.AddArc(new Arc(a.Ilabel, a.Olabel, a.Weight, s));
}
}
}
var stateIndex = p.GetId();
r[stateIndex]++;
if ((r[stateIndex] == n) && (p.FinalWeight != semiring.Zero))
{
break;
}
if (r[stateIndex] <= n)
{
for (var j = 0; j < p.GetNumArcs(); j++)
{
var a = p.GetArc(j);
var cnew = semiring.Times(c, a.Weight);
var next = new Pair <State, float>(a.NextState, cnew);
previous.Put(next, pair);
queue.Add(next);
}
}
}
return(res);
}
